Transformer shorting device

ABSTRACT

A small size transformer comprises a short-circuit inducing device placed within a coil of coils of the transformer and electrically connected between a primary coil and a power supply. The device comprises a spacer of an electrically insulative material capable of melting at a given temperature, and a pair of conductors electrically insulated from each other by the spacer, but closely spaced enough to contact each other upon melting of the spacer. This arrangement prevents the burning of the transformer upon occurrence of an overcurrent flow through or short-circuit condition across the transformer coils by disconnecting the primary coil from the power supply.

United States Patent Tone [4 1 Oct. 24, 1972 [73] Assignee: TokyoKeldenlkl Kabushikl Keisha,

Ota-ku, Tokyo, Japan 221 Filed: Feb. 3, 1971 [211 Appl.No.:1l2,356

[30] Foreign Application Priority Data Feb. 4, 1970 Japan ..45/11614 May11, 1970 Japan ..45/45823 [52] US. Cl ..3l7/15 [51] Int. Cl. ..H02h 7/04[58] field otSearch ..317/l5 [56] References Cited UNITED STATES PATENTS2,956,210 10/1960 Yatsushiro...................317/15 PrimaryExaminer-J. D. Miller Assistant Examiner-Harry E. Moose, Jr.Attorney-Ernest A. Greenside ABSTRACT A small size transformer comprisesa short-circuit inducing device placed within a coil of coils of thetransformer and electrically connected between a primary coil and apower supply. The device comprises a spacer of an electricallyinsulative material capable of melting at a given temperature, and apair of conductors electrically insulated from each other by the spacer,but closely spaced enough to contact each other upon melting of thespacer. This arrangement prevents the burning of the transformer uponoccurrence of an overcurrent flow through or short-circuit conditionacross the transformer coils by disconnecting the primary coil from thepower supply.

12 Claims, BDraWingFigures PATENTEDncr 24 m2 SHEEI 2 0F 2 FIG. 8

TRANSFORMER SHORTING DEVICE The invention relates to a small sizetransformer for use primarily in electrical communication system orother similar applications, and more particularly, to such a transformerwhich is provided with a device which prevents the occurrence of burningwith an abnormal temperature rise in the coils.

Abnormal temperature rise within a transformer as caused by overload orshort-circuiting conditions may not only result in the burning of theassociated coils, but also generally involves the possibility to inducefire and electric shocks. Where such transformer is built in a largerapparatus, adjacently located components and interconnection wirestherein may be subject to the adverse influence of the high temperatureswithin the transformer. As a result, various characteristic demands areimposed on the transformer to provide sufficient security against suchdanger, and the Underwriter's standards in the US. require that thereoccurs no danger of fire or electric shock upon short-circuiting thesecondary side of a transformer with 120V, 60I-IZ applied to the primaryside thereof.

It is known to connect a temperature sensitive fuse comprising a lowmelting metal in the service lines to a transformer and locate it incontact with the outer surface of the transformer, thereby serving theprevention of burning. Thus upon occurrence of an overcurrent to causean abnormal temperature rise, the thermal energy conducted from theinterior of the coils to the outer surface causes the fuse to be meltedfor disconnection of the transformer from the power supply. While thisrepresents a simple procedure, it is known to have certain drawbacks.Thus, the temperature fuse is inactive to a local overheating of thetransformer coils, in par ticular when such abnormal temperature riseoccurred at a position within the coils remote from the location of thefuse, or if it could respond to such occurrence, the response involves alarge time delay. This is undesirable in view of the difiiculty inherentto such sort of fuse to ensure a correct timing of action. Consequentlythere remains the danger for the transformer coils to burn before thetemperature fuse can be fused. Placing the temperature fuse within thetransformer would overcome such disadvantage, but is impracticable inview of the necessity to house the temperature fuse in a separate casingto secure a sufficient space to allow fusing of the low melting metal,which space cannot be obtained with usual transformer construction. Inaddition, the temperature fuse must be mounted in a restricted positionor attitude, and this necessitates its mounting on the exterior of thetransformer.

Accordingly, it is an object of the invention to provide a transformerwhich completely eliminates the above mentioned disadvantages of theprior art.

It is another object of the invention to provide a transformer providedwith a short-circuit inducing device arranged to produce a short-circuitcondition across the primary coil automatically when the temperaturewithin the coils exceeds a predetermined level, thereby disconnectingthe primary coil from a power supply by the operation of the device tocause a breakage therein.

It is a further object of the invention to provide a transformerprovided with the short-circuit inducing device which is simple inconstruction and is flat or linear in shape together with sufficientflexibility to permit it to be inserted into either coil together withits lead wires.

In accordance with the invention, the opposite ends of a primary coil ofa transformer are connected with the respective service lines through ashort-circuit inducing device that is placed in said coil or the othercoil or between the both coils, with the short-circuit inducing devicebeing operable in response to the temperature of the location in whichit is mounted to disconnect the primary coil from its associated servicelines. The short-circuit inducing device comprises a spacer of anelectrically insulative material capable of melting at a giventemperature, and a pair of conductors insulated from each other by thespacer, but closely spaced enough to contact each other upon melting ofthe spacer, the conductors forming at least one cross-over point.

It is desirable that with a temperature range experienced during thenormal use of the transformer, the spacer undergoes no or little changein its nature, but rapidly melts at a given temperature higher than thetemperature range mentioned above. Suitable material for such a spacercan be selected from a group of thermoplastic resins such as polyester,polypropylene, nylon or the like. It will be understood by those skilledin the art that the term a given temperature depends upon thespecification of a transformer such as power and voltage ratings andcoil insulation ratings. Since the spacer should electrically insulatethe pair of conductors from each other during normal operation of thetransformer, it may comprise a film interposed between the conductors orcomprise a coating on the conductors. Each of the conductors in theshort-circuit inducing device may comprise the end portions of or leadwires to the primary coil with their customary insulation removed.Alternatively, the short-circuit inducing device may be separate fromthe primary coil and connected to the opposite ends thereof by itsconductors.

While it is not intended to disclose herein all of such possiblemodifications and variations, the features and advantages of theinvention will be best understood from the following detaileddescription of specific embodiments thereof with reference to thedrawings, wherein:

FIG. 1 is a schematic circuit diagram of a transformer incorporating theshort-circuit inducing device according to the invention;

FIG. 2 is a section of a transformer embodying the principle of theinvention;

FIG. 3 is a perspective view of the short-circuit inducing device shownin FIG. 2;

FIG. 4 is a perspective view illustrating a modification of the deviceshown in FIG. 3;

FIG. 5 is a perspective view of a short-circuit inducing device whichincludes conductors comprising bundies of fine wires;

FIG. 6 is a perspective view of a device similar to that shown in FIG. 3except that conductors are pinned to the spacer;

FIG. 7 is a perspective view of a device similar to that shown in FIG. 6except that pins are replaced by adhesive tapes; and

FIG. 8 is a perspective view of a slotted spacer.

Referring to the drawings, the transformer circuit embodying theprinciple of the invention is shown in FIG. 1 wherein it will be notedthat the circuit is conventional except that at least one short-circuitinducing device generally shown at 3 is connected between a power supply1 and a primary coil 2. A load 5 is shown connected across a secondarywinding 4. The short-circuit inducing device 3 is specifically shown invarious forms in FIGS. 3 to 8 inclusively, and comprises a spacer 6 ofan electrically insulative material capable of melting at a giventemperature, and a pair of conductors 7, 7 electrically insulated fromeach other, but closely spaced enough to contact each other upon meltingof the spacer and forming at least one crossover point. The pair ofconductors 7, 7 are connected so as to constitute the lines between thepower supply 1 and the primary coil 2.

In FIG. 2, the short-circuit inducing device 3:5 shown as mounted withina transformer coil. In the example shown, the transformer is ofconcentric type, comprising a center core 8 around which is arranged aspool 9 receiving the primary coil 2 and the secondary coil 4. Theshort-circuit inducing device 3 is placed intermediate the primary andsecondary coils 2 and 4, as surrounded by insulations l and 11. Whilethe shortcircuit inducing device 3 is exaggerated in the drawing tooccupy a substantial space, it should be understood that this showing isfor the purpose of clarity, but that in practice, it is rolled betweenthe insulations l0 and II without the need for a special space therefor.It will be also noted that the device 3 may be placed within either coilinstead of being interposed between the coils, and hence the particularposition it is located is a matter of choice. It will also readily occurto these skilled in the art that a plurality of short-circuit inducingdevices distributed throughout the coils may be connected in series. Itshould be emphasized that the form or type of the transformer does notform any part of the invention. The short-circuit inducing device 3 ofthe invention need only and can be located anywhere within the coilswhere it is most convenient to sense the temperature therein.

Specific embodiments of the short-circuit inducing device are shown inFIGS. 3 to 8 wherein same reference characters are used throughout theseFigures to denote like parts. In the arrangement of FIG. 3, the spacer 6is in the form of a film and the pair of conductors 7, 7 are solidwires. Parts of the conductors smeared out in black representsinsulative coatings on the enamelled solid wires. The pair of conductors7, 7 have oppositely oriented bends l2, 12 on the opposite surfaces ofthe spacer 6, thereby forming a pair of cross-overs 13, 13 in planprojection. These conductors 7, 7 are partially or entirely bonded tothe spacer 6 along their length on the spacer. In FIG. 4, thearrangement is similar to FIG. 3, but is advantageous in that it hasfour cross-overs 13 any of which can be effective to provideshort-circuit across the both conductors. FIG. shows the use of bundlesof fine wires for the conductors 7, 7. in this instance, the need forforming the cross-over as is produced with solid wires is in effecteliminated by spreading these fine wires.

In the operation of the devices illustrated in FIGS. 3 to 5, it is foundthat one or both of the conductors become interrupted upon melting ofthe film spacer. While this phenomenon is not completely understood, itis believed that upon melting of the spacer, there occurs a sparkdischarge across the pair of conductors at the cross-over to cause thebreakage or interruption in the conductors.

FIGS. 6 to 8 show the alternative methods of securing the pair ofconductors 7, 7 to the spacer 6. While in the preceding embodiments, theconductors 7, 7 have been bonded to the spacer 6 by means of anadhesive, several small pins 14 in FIG. 6 or adhesive tape segments inFIG. 7 may be used. FIG. 8 shows a slotted spacer 6, that is, the spaceris formed with grooves 16, 16 in its opposite surfaces which receive anddefine the location of the conductors 7, 7. Adhesive may be additionallyapplied to assure firm attachment.

In the transformer according to the invention, upon occurrence of anovercurrent flow through the transformer to cause abnormal temperaturerise within its coils which is sufficient to raise the temperature tothe melting temperature of the material from which the spacer is made,the spacer melts to cause contact between the pair of conductors locatedon opposite sides of the spacer, yielding a short-circuit at thatposition of contact. As a result, the primary coil is disconnected fromthe power supply to prevent the burning of the transformer.

Specific examples are given below in order to illustrate the invention.

EXAMPLE 1 transformer output: 10 watts The short-circuit conditionacross the conductors occured at l C.

EXAMPLE 2 10 watts I00 turns of 0.23 mm at wire 200 turns of 0.5 mm 45wire polypropylen film, 0.05 mm thick transformer output: primary coil:secondary coil: spacer:

The short-circuit condition occured at C.

As will be appreciated from the foregoing, the invention is practicablein a number of manners and the embodiments shown herein are merelyillustractive of the invention. Therefore, it should be understood thatfurther modifications and variations are possible without departing fromthe spirit of the invention as defined by the appended claims,

Having described the invention, what is claimed is:

1. A transformer comprising at least a primary and a secondary coilwinding respectively adapted for connection to a source of current and aload, and a shortcircuit inducing device within said windings andprovided with at least two independent conductors for connecting atopposed ends to said source of current and to said primary winding, saiddevice being constituted of an elongated planar spacer of anelectrically insulative material capable of melting at a predeterminedtemperature and carrying said independent conductors in spaced apartrelation on opposite sides of said spacer and coextensive therewithalong the longitudinal extent thereof, said conductors defining alongthe longitudinal length of the spacer multiple crossover points at whichelectrical contact between said conductors may be made upon melting ofsaid planar spacer.

2. A transformer comprising at least a primary and a secondary coilwinding respectively adapted for connection to a source of current and aload, and a shortcircuit inducing device within said windings andprovided with at least two independent conductors for connecting atopposed ends to said source of current and to said primary winding, saiddevice being constituted of an elongated planar spacer of anelectrically insulative material capable of melting at a predeterminedtemperature and carrying said two independent conductors in spaced apartrelation on opposite sides of said spacer and coextensive therewithalong the longitudinal extent thereof, one of the independent conductorson one side of the spacer having a series of undulations along thelongitudinal extent of the spacer defining peaks and troughs, the otherof the independent conductors on the other side of said spacer having aseries of undulations along the longitudinal extent of the spacer alsodefining peaks and troughs, with the peaks and troughs of theundulations of the other independent conductor occurring at the troughsand peaks respectively of said one conductor providing thereby, betweenthe peaks and troughs of the respective undulations of said conductors,a plurality of cross-over points at which electrical contact betweensaid conductors may be made upon melting of said planar spacer.

3. A transformer according to claim 2, in which the spacer is in theform of a film.

4. A transformer according to claim 3. in which the pair of conductorscomprise bundles of fine wires.

5. A transformer according to claim 3, in which the pair of conductorsare secured to the spacer by adhe- 81011.

6. A transformer according to claim 3, in which the pair of conductorsare secured to the spacer by pins struck into the spacer.

7. A transformer according to claim 3, in which the pair of conductorsare secured to the spacer by adhesive tapes.

8. A transformer according to claim 3, in which the spacer is formedwith grooves in its opposite surfaces for receiving the pair ofconductors therein.

9. A transformer according to claim 2, in which the spacer comprises athermoplastic resin.

10. A transformer according to claim 9, in which the thermoplastic resinis polyester.

11. A transformer according to claim 9, in which the thermoplastic resinis polypropylene.

12. A transformer according to claim 9, in which the thermoplastic resinis nylon.

1. A transformer comprising at least a primary and a secondary coilwinding respectively adapted for connection to a source of current and aload, and a short-circuit inducing device within said windings andprovided with at least two independent conductors for connecting atopposed ends to said source of current and to said primary winding, saiddevice being constituted of an elongated planar spacer of anelectrically insulative material capable of melting at a predeterminedtemperature and carrying said independent conductors in spaced apartrelation on opposite sides of said spacer and coextensive therewithalong the longitudinal extent thereof, said conductors defining alongthe longitudinal length of the spacer multiple cross-over points atwhich electrical contact between said conductors may be made uponmelting of said planar spacer.
 2. A transformer comprising at least aprimary and a secondary coil winding respectively adapted for connectionto a source of current and a load, and a short-circuit inducing devicewithin said windings and provided with at least two independentconductors for connecting at opposed ends to said source of current andto said primary winding, said device being constituted of an elongatedplanar spacer of an electrically insulative material capable of meltingat a predetermined temperature and carrying said two independentconductors in spaced apart relation on opposite sides of said spacer andcoextensive therewith along the longitudinal extent thereof, one of theindependent conductors on one side of the spacer having a series ofundulations along the longitudinal extent of the spacer defining peaksand troughs, the other of the independent conductors on the other sideof said spacer having a series of undulations along the longitudinalextent of the spacer also defining peaks and troughs, with the peaks andtroughs of the undulations of the other independent conductor occurringat the troughs and peaks respectively of said one conductor providingthereby, between the peaks and troughs of the respective undulations ofsaid conductors, a plurality of cross-over points at which electricalcontact between said conductors may be made upon melting of said planarspacer.
 3. A transformer according to claim 2, in which the spacer is inthe form of a film.
 4. A transformer according to claim 3, in which thepair of conductors comprise bundles of fine wirEs.
 5. A transformeraccording to claim 3, in which the pair of conductors are secured to thespacer by adhesion.
 6. A transformer according to claim 3, in which thepair of conductors are secured to the spacer by pins struck into thespacer.
 7. A transformer according to claim 3, in which the pair ofconductors are secured to the spacer by adhesive tapes.
 8. A transformeraccording to claim 3, in which the spacer is formed with grooves in itsopposite surfaces for receiving the pair of conductors therein.
 9. Atransformer according to claim 2, in which the spacer comprises athermoplastic resin.
 10. A transformer according to claim 9, in whichthe thermoplastic resin is polyester.
 11. A transformer according toclaim 9, in which the thermoplastic resin is polypropylene.
 12. Atransformer according to claim 9, in which the thermoplastic resin isnylon.